Method for producing asymmetric radial polymers

Abstract

The present invention is a process for producing predominately four-armed asymmetric radial block copolymers which contain predominately, on average, two arms which are copolymers of at least one conjugated diene and at least one vinyl aromatic hydrocarbon and two conjugated diene homopolymer or copolymer arms, said process comprising: (a) anionically polymerizing at least one conjugated diene monomer and at least one vinylaromatic hydrocarbon monomer to form a set of living polymer arms, (b) anionically polymerizing at least one conjugated diene monomer to form another set of living polymer arms, (c) coupling the one set of living polymer arms with a coupling agent which is selected from the group consisting of tetramethoxysilane and γ-glycidoxypropyltrimethoxysilane, (d) substantially completing the coupling reaction while leaving, on average, two unreacted coupling sites on the coupling agent, (e) adding the other set of living polymer arms to the product of d) and coupling the other set of living polymer arms to the first coupled set of polymer arms, and (f) optionally, hydrogenating the coupled polymer, either partially or fully.

We claim: 
     
       1. A process for producing a predominately four-armed asymmetric radial block copolymer which contains predominately two arms which are copolymers of at least one conjugated diene and a vinyl aromatic hydrocarbon and two conjugated diene homopolymer or copolymer arms, said process comprising: (a) anionically polymerizing at least one conjugated diene monomer and at least one vinylaromatic hydrocarbon monomer to form a set of living polymer arms,   (b) anionically polymerizing at least one conjugated diene monomer to form another set of living polymer arms,   (c) coupling one set of living polymer arms with a coupling agent which is selected from the group consisting of tetramethoxysilane and γ-glycidoxypropyltrimethoxysilane,   (d) substantially completing the coupling reaction while leaving, on average, two unreacted coupling sites on the coupling agent,   (e) adding the other set of living polymer arms to the product of d) and coupling the other set of living polymer arms to the first coupled set of polymer arms, and   (f) optionally hydrogenating the coupled polymer, either partially or fully.   
     
     
       2. The method of claim 1 wherein the coupling agent is tetramethoxysilane. 
     
     
       3. The method of claim 1 wherein one set of polymer arms is polyisoprene and the other set of polymer arms is a block copolymer of isoprene and styrene. 
     
     
       4. The method of claim 1 wherein one set of polymer arms is comprised of a block copolymer of styrene and isoprene and\or butadiene and the other set of polymer arms is comprised of isoprene and/or butadiene. 
     
     
       5. The method of claim 4 wherein the block polymer is hydrogenated to provide a polymer of which one set of polymer arms is comprised of a block copolymer of styrene and hydrogenated isoprene and/or hydrogenated butadiene and the other set of polymer arms is comprised of hydrogenated isoprene and/or hydrogenated butadiene. 
     
     
       6. The method of claim 4 wherein one set of polymer arms is comprised of a block copolymer of styrene and butadiene and the other set of polymer arms is polyisoprene. 
     
     
       7. The method of claim 6 wherein the block copolymer is partially hydrogenated to provide a polymer of which one set of polymer arms is comprised of a block copolymer of styrene and hydrogenated butadiene and the other set of polymer arms is partially hydrogenated polyisoprene. 
     
     
       8. The product of the process of claim 1. 
     
     
       9. The product of the process of claim 2. 
     
     
       10. The product of the process of claim 3. 
     
     
       11. The product of the process of claim 4. 
     
     
       12. The product of the process of claim 5. 
     
     
       13. The product of the process of claim 6. 
     
     
       14. The product of the process of claim 7.